The present invention relates to a method for making a colored multilayer composite by laminating to each other, and curing, two or more radiation-curable layers, one of these layers being a clear outer layer and the other layers being equipped with color pigments, and also to a colored multilayer composite of this type, produced by the method.
WO 94/09983 has disclosed that colored vehicle parts can be produced with at least two different shades by transfer onto the vehicle parts of colored acrylic layers which have been applied to casting films. A laminate of this type is composed of a first polyester supporting layer, of a clear layer made from an optically clear polymer which comprises fluorinated hydrocarbon resin and acrylic resin, the clear layer having been applied on the surface of the supporting layer, and also of a binder layer and of a color layer made from chlorinated polymer with dispersed color pigments. Laminated onto the color layer is a second polyester supporting layer with an adhesive layer. This laminate takes the form of a multilayer composite and is applied to vehicle parts using techniques associated with pressure-sensitive self-adhesives, followed by removal of the first supporting layer abutting the clear layer, so that the clear layer forms a weather-resistant outer layer of the laminate. The PVC-containing color layer is flexible at room temperature and permits dimensional change within the laminate, which can therefore be laminated onto vehicle parts of three-dimensional shape. For durable and firm adhesive anchoring of the color layers, this laminate requires intermediate layers made from specific adhesives which have to fulfill certain preconditions.
EP 0535504 B1 discloses a process for image transfer to coated surfaces, in particular those of timber-based materials, the surface being coated with a polymeric layer made from low-molecular-weight polymers and requiring curing by irradiation with electrons. The polymeric layer is brought into contact with a transfer medium bearing color pigment, with exposure to heat. There is diffusion of the color pigments into the polymeric layer. The irradiation with electrons cures the polymeric layer, crosslinking being undertaken with a radiation dose of from 40 to 80 kGray.
It is an object of the invention to provide a method which produces an at least two-coloured multilayer composite, can be carried out cost-effectively on an industrial scale and which moreover manufactures the multilayer composite without adhesive layers and produces a multilayer composite whose decorative properties are durably resistant to the effects of weathering.
According to the invention, the manner of achieving this object comprises, in a first step, partially curing the radiation-curable layers applied to supporting layers, and in a second step, completely curing the radiation-curable layers.
The features of the method of the invention are that in the first step, the first radiation-curable layer, equipped with color pigments, is applied to a first supporting layer, that the second radiation-curable layer, equipped with color pigments, is applied to a second supporting layer, where the color pigments of the first layer differ from those of the second layer, that the two supporting layers are laminated, with the radiation-curable layers facing toward one another, to give a multilayer composite, and the radiation-curable layers are partially cured, and that in the second step, the multilayer composite is laminated with a plastic film to which a radiation-curable clear outer layer is applied, which faces toward the multilayer composite, and that the mutually abutting layers are completely cured.
In executing the method, the partial curing and the complete curing of the layers is undertaken with the aid of actinic radiation. The actinic radiation used here comprises accelerated electrons, UV radiation in the wavelength region from 50 to 480 nm or X-ray radiation in the wavelength region from 0.05 to 8.0 nm.
In another embodiment of the method, use is made of radiation-curable layers based on C1-C6-alkyl acrylates and/or methacrylates, in particular those based on methyl acrylates or on ethyl acrylates and/or methacrylates.
In one embodiment of the method, the dose of actinic radiation in the steps is adjusted so that the amount of radiation required for the complete curing of the radiation-curable layers is not applied until the final irradiation stage.
If the amount of radiation theoretically needed for complete curing has been reached prior to the final irradiation stage, the bond strength of the clear outer layer can be adversely affected.
Further embodiments of the method arise from the measures described in claims 7 to 15.
The invention uses the method to produce a two- or multicolored multilayer composite which is composed of a supporting layer with a smooth regular surface, which is a plastic film or is a phenolic-resin-impregnated paper web, and of two or three acrylic-based layers laminated to one another and radiation-cured and comprising different color pigments, and of an acrylic-based clear outer layer, and also of a peelable plastic film as protective layer.
A multilayer composite of this type may be a decorative coating bonded to plates or panels made from layers of paper saturated with phenolic resins and/or with melamine resins, or made from cardboard packaging, from wood, from plastics, from resin-saturated compacted wood chips or the like, to give weather-resistant panels for outdoor use.